Black Rat

Introduction

The sewer rat (Rattus rattus), also known as the black rat or roof rat, is one of the most widespread and adaptable rodents in the world. Commonly found in urban areas across North America, these rodents are known for living in sewers, attics, warehouses, docks, and other human structures. Unlike wood rats or voles, sewer rats are invasive, aggressive, and a major vector for disease, making them one of the most serious urban pests.

Taxonomy:

• Order: Rodentia

• Family: Muridae

• Genus: Rattus

• Species: Rattus rattus

Physical Characteristics:

• Size: 16–20 inches (40–50 cm) including the tail

• Weight: 5–12 ounces (140–340 g)

• Appearance:

  • Slender body with a long, hairless tail (tail often longer than the body)

  • Fur is dark brown to black

  • Pointed nose and large, rounded ears

Habitat and Distribution:

• Found in urban environments worldwide, especially around docks, sewers, and older buildings

• Known for climbing and nesting in elevated areas like attics, rafters, and rooftops

Adaptations:

• Excellent climbers and jumpers

• Highly adaptable to a wide variety of food sources and environments

• Thrive in close association with humans, using sewers and utility lines as travel corridors

• Activity: Primarily nocturnal

• Nesting: Nest in attics, rafters, walls, warehouses, sewers, and vegetation close to buildings

• Territoriality: Live in colonies with structured social hierarchies

• Ecological Role:

  • Opportunistic scavengers feeding on human waste, food, and garbage

  • Known carriers of numerous zoonotic diseases

• Breeding occurs year-round in warm climates

• Gestation: ~21–23 days

• Litter size: 5–10 young per litter

• Can produce up to 6 litters per year

• Sexual maturity: 2–3 months

• Lifespan: 1–2 years in the wild

• Diet: Omnivorous; will eat almost anything, including:

  • Garbage and food waste

  • Small animals (birds, reptiles)

  • Pet food, grains, fruits, and vegetables

• Their ability to survive on a variety of foods makes them highly resilient pests

Trapping & Control

Trapping Tips:

Trap Choice:

Heavy-duty snap traps or multi-catch traps

Glue boards are less humane and less effective

Bait Selection:

Peanut butter, dried fruit, bacon, or fish-based baits

Fresh pet food can also work well

Trap Placement:

Place traps along walls, in dark corners, near burrows, or along known travel paths

Roof rats prefer elevated areas, so set traps in attics or rafters

Frequency:

Check traps daily and reset as needed

Signs of Sewer Rat Activity:

• Droppings: Larger than mouse droppings (½–¾ inch), capsule-shaped, often near food sources or along walls

• Gnaw Marks: Chewed wires, wood, pipes, and stored goods

• Burrows: May burrow near foundations, under sidewalks, or in sewers

• Grease Marks: Oily rub marks along walls and baseboards

• Noises: Scratching, gnawing, or scurrying sounds, especially in walls or ceilings at night

• Pet Behavior: Cats and dogs may become alert to areas with rat activity

Health Risks:

• Sewer rats are known carriers of:

  • Leptospirosis

  • Salmonella

  • Rat-bite fever

  • Plague (historically)

  • Hantavirus

• They also carry fleas and mites, which can transmit other diseases

Exclusion & Prevention:

• • Seal gaps larger than ½ inch with metal flashing or hardware cloth

  • Secure garbage in heavy-duty containers with tight-fitting lids

  • Eliminate food and water sources: clean up crumbs, store food in sealed containers, fix leaks

  • Trim tree branches 6–8 feet away from roofs to prevent roof access

  • Install vent and chimney screens